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Spatial genetic structure in Milicia excelsa (Moraceae) indicates extensive gene dispersal in a low-density wind-pollinated tropical tree

Authors

  • J.-P. BIZOUX,

    1. Laboratory of Ecology, Gembloux Agricultural University, 2 Passages des Déportés, 5030 Gembloux, Belgium
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    • 1

      These authors have equally contributed to the study.

  • K. DAÏNOU,

    1. Laboratory of Tropical and Subtropical Forestry, Gembloux Agricultural University, 2 Passages des Déportés, 5030 Gembloux, Belgium
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    • 1

      These authors have equally contributed to the study.

  • N. BOURLAND,

    1. Laboratory of Tropical and Subtropical Forestry, Gembloux Agricultural University, 2 Passages des Déportés, 5030 Gembloux, Belgium
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  • O. J. HARDY,

    1. Behavioural and Evolutionary Ecology Unit – CP 160/12, Faculté des Sciences, Université Libre de Bruxelles, 50 Av. F. Roosevelt, 1050 Brussels, Belgium
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  • M. HEUERTZ,

    1. Behavioural and Evolutionary Ecology Unit – CP 160/12, Faculté des Sciences, Université Libre de Bruxelles, 50 Av. F. Roosevelt, 1050 Brussels, Belgium
    2. Department of Forest Systems and Resources, Centre of Forest Research CIFOR-INIA, Carretera de la Coruña km 7.5, 28040 Madrid, Spain
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  • G. MAHY,

    1. Laboratory of Ecology, Gembloux Agricultural University, 2 Passages des Déportés, 5030 Gembloux, Belgium
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  • J.-L. DOUCET

    1. Laboratory of Tropical and Subtropical Forestry, Gembloux Agricultural University, 2 Passages des Déportés, 5030 Gembloux, Belgium
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  • The various laboratories involved in this work have collaborated for many years to study the ecology and population genetics of timber trees in the tropical forests of Central Africa. The aim of these research projects is to contribute to the development of best management practices to ensure the sustainability of local forest resources.

K. Daïnou, Fax: +32 (0)81 622342; E-mail: dainou.k@fsagx.ac.be

Abstract

In this study, we analysed spatial genetic structure (SGS) patterns and estimated dispersal distances in Milicia excelsa (Welw.) C.C. Berg (Moraceae), a threatened wind-pollinated dioecious African tree, with typically low density (∼10 adults/km2). Eight microsatellite markers were used to type 287 individuals in four Cameroonian populations characterized by different habitats and tree densities. Differentiation among populations was very low. Two populations in more open habitat did not display any correlation between genetic relatedness and spatial distance between individuals, whereas significant SGS was detected in two populations situated under continuous forest cover. SGS was weak with a maximum Sp-statistic of 0.006, a value in the lower quartile of SGS estimates for trees in the literature. Using a stepwise approach with Bayesian clustering methods, we demonstrated that SGS resulted from isolation by distance and not colonization by different gene pools. Indirect estimates of gene dispersal distances ranged from σg = 1 to 7.1 km, one order of magnitude higher than most estimates found in the literature for tropical tree species. This result can largely be explained by life-history traits of the species. Milicia excelsa exhibits a potentially wide-ranging wind-mediated pollen dispersal mechanism as well as very efficient seed dispersal mediated by large frugivorous bats. Estimations of gene flow suggested no major risk of inbreeding because of reduction in population density by exploitation. Different strategy of seed collection may be required for reforestation programmes among populations with different extent of SGS.

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